In an electric disc grinder, there is provided, between a driven gear and a spindle in a torque transmission system, a C-shaped spring member capable of elastic deformation in a diameter enlarging direction. With respect to the rotating direction, the spring member is engaged with a driving protrusion of the driven gear and a driven protrusion of a joint sleeve of the spindle; when transmitting the rotation of the driven gear to the spindle, the spring member undergoes elastic deformation in the diameter enlarging direction depending on the driven side load, thereby mitigating the starting shock. An abutment surface of the driven protrusion is formed as an inclined surface causing an end portion of the spring member contacting with the abutment surface to slide radially outwards. As a result, the spring member can easily undergo elastic deformation in the diameter enlarging direction.